1. Technical Field
The present invention pertains to lenses. In particular, the present invention pertains to a lens collimator, preferably for optical communication systems, that provides optical signals with reduced aberrations. The lens collimator includes a plurality of lens elements that provide an increased quantity of surfaces for optical signal reflections and refractions to occur within the lens optical path, thereby enabling the lens collimator to cancel out adverse effects (e.g., aberrations, etc.) from the resulting optical signals or beam.
2. Discussion of Related Art
Optical communication systems employ optical or light signals to transfer information between system sites. Interconnection between local system sites may employ media, such as fiber optic cables, to transport the optical signals. With respect to remote system sites, the optical signals may be transmitted in the surrounding environment between transmitting and receiving units. These units typically employ lenses to produce the optical signals in a desired format. For example, a transmitting unit lens typically receives narrow or focused optical signals from a carrier (e.g., fiber optic cable, etc.) and produces collimated or parallel optical signals for transmission. Conversely, a receiving unit lens receives the collimated or parallel optical signals and focuses the signals onto a narrow carrier (e.g., fiber optic cable, etc.) for subsequent processing.
Lenses with spherical surfaces are typically employed by the transmitting and receiving units to produce the desired optical signals. However, these types of lenses produce aberrations that degrade the produced optical signals. The aberrations vary depending upon the dimensions and materials of the lens. In order to reduce aberrations, lenses are designed to reflect and refract the optical signals in a manner that cancels out the undesirable effects. Generally, the greater the quantity of surfaces within and different materials of the lens the better the lens performance that can be achieved.
Conventional lens designs generally implement a linear optical path. However, some may employ a folded optical path, where the quantity of folds is limited. For example, U.S. Pat. No. 4,121,890 (Braun) discloses a laser rangefinder tester. A thick lens or prism with at least one spherical shaped surface is utilized in conjunction with a glass fiber delay line to create a sensitivity, boresight and range accuracy test unit for a laser rangefinder. A light ray is reflected within the prism and is gradually focused to a focal point due to a curved reflective surface. The prism is designed to provide a minimum beam diameter at the focal point which is located just outside the prism, where the beam is injected into an input end of an optical fiber or waveguide of a delay unit. The delay unit produces a simulated range return pulse for the rangefinder that travels through the prism as described above.
The above lenses suffer from several disadvantages. Although the above types of lenses are generally easier to fabricate and less expensive, the dimensions and weight of these lenses are usually significant. Since optical systems are typically employed with other components and/or in areas of limited space (e.g., a turret on planes and/or helicopters, etc.), the dimensions and weight of the lens becomes important. This is especially pertinent since these lens characteristics have a ripple type effect on the size and weight of system components housing the lens. Further, the reduced quantity of folds or reflections and refractions in a lens optical path has a deleterious effect on aberrations, thereby producing a degraded beam or requiring additional components to compensate for the adverse effects. Generally, a greater quantity of reflections and refractions within a lens optical path reduces aberrations. Enhancing the quality of reflections in a single element lens significantly increases fabrication and associated costs. For example, diamond turning is likely to be employed, where the single element lens requires multiple aspheric curvatures on different portions of each surface. Post-turning polishing in these circumstances is extremely difficult and tends to adversely affect the surface accuracy.
The present invention lens collimator includes additional elements and surfaces to provide an enhanced quantity of reflections and refractions within the lens optical path in order to significantly cancel out the spherical aberrations. This permits surface curvatures and lens element glass types to be optimized to reduce total lens spherical aberration while minimizing the size of the central obscuration.